1. Field of the Invention
The invention relates to a method for producing silicon nitride films and more particularly relates to a method for producing silicon nitride films by chemical vapor deposition (CVD).
2. Description of the Prior Art
Silicon nitride films have excellent barrier properties and an excellent oxidation resistance and as a consequence are used in the fabrication of microelectronic devices, for example, as an etch-stop layer, barrier layer, or gate dielectric layer, and in oxide/nitride stacks.
Plasma-enhanced CVD (PECVD) and low-pressure CVD (LPCVD) are the methods primarily used at the present time to form silicon nitride films.
PECVD is typically carried out by introducing a silicon source (typically silane) and a nitrogen source (typically ammonia, but more recently nitrogen) between a pair of parallel plate electrodes and applying high-frequency energy across the electrodes at low temperatures (about 300° C.) and low pressures (0.1 torr to 5 torr) in order to induce the generation of a plasma from the silicon source and nitrogen source. The active silicon species and active nitrogen species in the resulting plasma react with each other to produce a silicon nitride film. The silicon nitride films afforded by PECVD typically do not have a stoichiometric composition and are also hydrogen rich and accordingly exhibit a low film density, a fast etching rate, and a poor thermal stability.
In contrast to the preceding, LPCVD uses low pressures (0.1 to 2 torr) and high temperatures (800° C. to 900° C.) and produces silicon nitride films with a quality superior to that of the silicon nitride films produced by PECVD. At the present time silicon nitride is typically produced by LPCVD by the reaction of dichlorosilane and gaseous ammonia. However, ammonium chloride is produced as a by-product in the reaction of dichlorosilane and gaseous ammonia in this LPCVD procedure: this ammonium chloride accumulates in and clogs the reactor exhaust lines and also deposits on the wafer. Moreover, existing LPCVD technology suffers from a slow rate of silicon nitride film growth and has a high thermal budget. In order to reduce this thermal budget associated with the production of silicon nitride films, a method has very recently been developed that produces silicon nitride films by reacting ammonia with hexachlorodisilane used as a silicon nitride precursor. This method, however, suffers from a pronounced exacerbation of the problems cited above due to the large amounts of chlorine present in hexachlorodisilane. Silicon-containing particles are also produced by this method, which results in a substantial reduction in the life of the exhaust lines. Finally, this method can provide good silicon nitride films (high quality, good step coverage ratio, low chlorine content) at excellent growth rates when the reaction temperature is, for example, 600° C., but these characteristics suffer from a pronounced deterioration when a reaction temperature ≦550° C. is used.
Methods that use trisilylamine as a precursor in the formation of silicon nitride films by CVD have recently been disclosed. Thus, a method is disclosed in U.S. Pat. No. 6,566,281 B1 in which silicon nitride is produced by flowing trisilylamine and ammonia over substrate. A method is disclosed in U.S. Pat. No. 6,630,413 B1 in which silicon nitride film is produced by reacting trisilylamine with a nitrogenous compound such as an amine. Since trisilylamine lacks chlorine, these methods are free of the problems noted above that arise due to the generation of ammonium chloride by-product.